Boards & Capes cards on index.rst using sphinx-design extension.

* List all boards in top-level ToC
* Fix BeagleConnect headings and general clean-up

Origianl content copied and convertet to rst from https://github.com/MarkAYoder/PRUCookbook, All credits to Author: Mark A. Yoder (Mark.A.Yoder@Rose-Hulman.edu)

Changed from bone-cook-book to beaglebone-cookbook

Thanks to Vedant and Krishna for the contribution. With this commit, all existing and new beagleboard.org software projects will now be added to Projects section.

* Move getting-started as an include item in index
* Fix a few links/terms in index

New sphinx documentation setup for BeagleBoard docs wesbite.